Traffic control signal



lmgm,1937. T. P. PREIST EN. 2,091,653

TRAFFIC CONTROL SIGNAL Filed Jan. m, 1935 CAMS F PHASE A2 Vernon Imaam. 5 Amun LzAvmG lun' To ColvrRo/.LE Ar AoJAcE/v-r /mrsRsecr/om I. ZI

THOMAS PHmP Pnem INVENTORS XAZ. v .W ALFrzBElP Perzcv BMLEY RENsHAw xmy YAz v Patented Aug. 31, 1937 Unirse s'rarss PATENT O'FFIQ 2,091,653i TRAFFIC CONTROL SIGNAL don, England Application January 10, 1935, Serial No. 1,124 In Great Britain January 20, 1934 ii pimms.

The present invention relates to trahie control signals for use at road junctions 'or the like, and is more particularly concerned with systems in i which controllers at adjacent intersections are *f interlinked so as to function under certain conditions in related sequence. The invention finds particular application in connection with systems employing vehicle-actuated ldevices such as contact-making pads let into the road surface, but is not limited thereto.

The chief object of the invention is to provide a system for controlling traffic at adjacent intersections on the same roadway in which theoperations of the controllers at the said intersections l5 are interlinked to prevent traffic congestion arising due to traffic filling that portion of the roadway which connects two `intersections together.

According to one feature of the invention in a traic control system including a` plurality of ad- 'if'20 `jacent intersections on a main road each intersection being controlled by a controllerindividual thereto which is linked to one of more other con-- trollers the linking between adjacent controllers serves to ensure that main road traffic' passing t`-iz5 one intersection shall receive preferential treatment at the succeeding crossing.

According to another feature of the invention in a traffic control system employing vehicle detectors for controlling the operation of the signals "30 and arranged so that a continuous stream of vehicles in one road will maintain right of way for that road up to a maximum period after the arrival of traffic on an intersecting road the maX- imum periodis arranged to be reduced for waiting i 35 traffic on a particular intersecting road if there is 4a predetermined trai-hc distribution at an adjacent crossing.

A further feature of the invention is that in a trafiic control system including at least two inter- 40 sections on a main road each intersection being controlled by a controller individual, thereto with which are associated vehicle detectors operation ofthev detector located in the main road approaching the second intersection While right of lo Way is being denied to the main road there causes the controller thereat to transmit a signal tol the controller at the rst intersection and if the latter isin a particular condition the maximum period for which right of Way can be denied to the main road at the second intersection is reduced.

The invention will be better understood from the following description of one method of carryiing it into effect, reference being had to the ac.-

.55 Companying drawing in which:

(Cl. TVI- 337) Fig. l is a plan of `a road withtw'o adjacent intersections.

Fig. 2 is a schematic diagramof .the apparatus for one of the intersections. v

It will be understood that the control apparatus for the other intersection is similar. f f In Fig. l the respective intersections' are designated X and Y, and they may be considered for the purpose of this description asformed by two secondary roads intersectingia main, road having a. comparatively heavylow of through traniic. It may be further assumed that the portion of the main road lying between 4the intersections is of such short length .that itis impossible to consider the stopping of main .road trafc therein for any length of time', 'becausefofthe danger of the vehicles accumulating andblocking the cross traflic at the intersection .behind.` It is assumed that the same danger doesnot occur in f control connection with vehicles arrivingffrorii .the seci? ondary roads owing to the small amount of' turning tramo, consequently, no special'precautions are necessary and for such trafcth'e controllers are allowed to function independently'. The essential function of the interlinkihgtherefore'is to ensure that main road trafc which enters the area in question shall be given immediate right of way at' the succeeding intersection; that is, for instance, vehicles that approach lthe X intersection from the direction of 'Y shall'be given right i' of way promptly at X in spite oit" demands of cross traffic at X. Thus in the event ofa vehicle actuating detector XAZ while right Aofway' is being denied to the main road .at `X and while right of way is being accorded to' the main roadv at Y, will quickly be accordedv right of w'ay in order that such vehicle and vehicles'followingit from Y will not be delayed tocause a'line of stopped traflfc suflicient to blockth'e Y inter'- section. This is achieved by the operation of 'the detectors XA! and YAZ or YAI and'XAZ in sequence, which completes the interlink'ingcir'cuit so that the existing setting of the succeeding'conl troller is overruled in favour ofthe main road tralic. l

It will be understood that preferably-"both intersections are equipped with' Vehicle actuated controllers. These controllers are provided with switches by means of Which in the absenceof trahie the right of way maybe caused torevert to and rest on either the main road 'or' the cross road as desired upon the cessation oftrail-lo on the opposite road, or the controls may7 be' caused to rest in the position with right of Way accorded to the road to Which it Was last called'by trafc'.

If tranic on the cross road is light compared with that on the main road, right of Way will be accorded the latter for a greater portion of the time.

These controllers are modied in accordance with the invention to peremptorily shorten the maximum time limit for cross tranic at one of the intersections, (the second intersection, for instance) so that when traic on the main road is approaching the latter from the other intersection there will be an interlinking eiTect between the two controllers, but for traiiic approaching the second intersection along the main road from the opposite direction the controller is permitted to operate normally without any special action corresponding to that provided for traiic approaching from the rst intersection, X. In accordance with the invention the controllers may correspondingly be modied so that tranic passing from the second intersection Y toward the iirst intersection X will peremptorily shorten the maximum period of cross road tramo at the latter.

A description will now be given of the circuit operations and it should first be mentioned that the controller about to be described is provided with a number of sets of contacts operated by a cam shaft which is moved step by st-ep by means of a solenoid. The solenoid is controlled from a timing circuit emplcyin@ a neon lamp (or other type gas discharge tube) condenser combination, the timing of which is varied under the control of vehicle detectors located in the roadway. Initial and maximum timing circuits are also provided which respond to the passage of the vehicles over the detectors.

Referring now to the circuit, it will be noted from Fig, 2 that the controller is arranged for operation from alternating current mains and that suitable rectifying arrangements are provided in the form of a thermionic valve VLV and transformer )QPR by means of which direct current is obtained for operating the neon lamps and this is supplied from the terminal marked positive in a rectangle. Conveniently the live main of the alternating current supply is connected to the appropriate tapping point TB on the transformer, while the grounded main which appears in other parts of the drawing as minus in a circle and rectangle is connected to the terminal TA. By suitable windings the transformer XFR is arranged to supply a reduced potential of 12 volts and this is available at the terminal TP for operating the relays in the controller. The lament of the valve is lit from a similar winding` The chart at the right of Fig. 2 shows the positions of the cam shaft in which the various cam contacts are operated, a black circle or bar indicating that the contact is closed. The various interval adjusting switches shown at the top of the drawing are wired to appropriate tapping points on the two common resistances 2t and 2i respectively. Common resistance 2t is built up for the most part of units each of '200,000 ohms resistance connected in series, each unit representing a charging time of the condenser QA equivalent to one second. The other common resistance 2l is similarly constructed but in this case the units are of much higher value, for instance, one or two megohms, and provide for long time periods such as are required for maximum timing purposes.

It will be assumed that the controller illustrated is the one serving intersection X in Fig. l and that the cam shaft is standing in position 3 giving right of way to phase B, i. e. the secondary phase B detector within short intervals thus produces corresponding resetting of the charge on condenser QA.

Suppose now that a vehicle arrives on the main road and crosses the phase A detector XAI. Road relay E is operated and locked over its armature el and cam contacts Cl8 and at armature e2 it prepares a circuit for operating relay A, while at the same time completing a charging circuit over the cam contacts Cil for the condenser QB of the maximum timing circuit which is controlled at this period over the maximum interval switch MXB. Subsequently due either to a gap in the phase B trafiic or the expiration of the maximum period either condenser QA or condenser QB will charge to the striking potential of the neon lamp FA or FB whereupon either relay A or B as the case may be is operated to energize the solenoid S which advances the cam and the cam shaft is stepped into position 5. In

this position the amber lamps are extinguished and the red and green lamps RB and GA are lighted to stop the B phase traiiic and give right of way to the A phase traino on the main road.

In order to provide a suiiicient period for the.

starting up of any A phase traiic which may be waiting an initial interval is now timed over the switch INA after which the cam shaft steps to position 6. Here no change is made in the signal lamp circuits but the locking circuit of road relay E is opened at cam contacts CIB so that this relay may operate intermittently under the control of the main road tramo to extend the right of way period. It wiil be understood that in this position in the event of actuation on the cross road and either the cessation of traino, or the expiration of the maximum period thereon if traic is continuous, the controller will shift from position t to the next position, l, thru action of lamp FA or FB respectively. The controller will proceed successively from position l the amber position leaving phase A into position 2 the initial interval for phase B, and then into position 3 the vehicle interval for phase B, through successive charging periods of the condenser QA and corresponding operation of the tube FA and the solenoid S, thus completing the tracing of one complete cycle of operation of the controller. For the further operation of the system under the interlinking arrangement it will be assumed, however, that the X controller has remained in position 6, and reference must now be had to the controller serving the intersection Y.

As already mentioned this controller is exactly similar to the X intersection controller and therefore the same circuit may be considered and for convenience of the description it will be assumed that the cam shaft is standing in position 3, giving right of way to the phase B traiiic at Y. Assuming that the main road traflic previously liberated at the X intersection during the main street green periods at X is to pass also through the Y intersection, this traffic will actuate the detector YA2 in Fig. 1 which corresponds to the phase A2 detector of the X controller. v

Considering the operation of this detector in relation to the circuit, it will be seen that the road relay F if not already operated immediately operates and locks up and performs similar functions to that of road relay E already described, and in addition at armature f4 prepares a circuit for the interlinking relay G. The circuit of relay G extends as shown over a pair of wires to the X controller and as this controller will be standing in either position 5 or 6 the circuit to relayG is completed over the cam contacts C8 shown in the dotted rectangle. It will be seen that the X controller at this time will be standing With its camshaft in either of these positions 5 or 6, the main road green period, since main road traflic has been passing thru X and approaching Y, therefore cam contacts C8 in the X controller will be closed and accordingly a circuit to operate relay G in the Y controller is ist completed. Relay G completes a reduced maximum timing circuit over the switch RMX and almost immediately this circuit becomes operative to step the cam shaft into position 4 regardless of the phase B trafiic. This operation proi duces the normal amber warning signal after which right of way is changed over in favour of the main road traffic which is thus enabled to proceed substantially Without interruption.

The interlinking feature also functions in the reverse directio-n from the XAZ detector and in these circumstances relay G o-f the X controller is operated over another pair of Wires extending from cam contacts C8 of the Y controller, to assure prompt return of right of way to the main road at X.

It should be explained that in these controllers the reduced timing of the maximum does not reduce the normal amber intervals since cam contact CIS is not closed in these periods. The timing of the reduced maximum may preferably also be adjusted not to interfere with the normal initial interval so as to assure that when relay G is operated upon or immediately after transfer of right of way to the cross road, cross road traflic will be assured of a. short protective minimum period. The interlinking feature is not effective in the case of turning traiiic from the main road and similarly in the case of turning trafc from the secondary roads, since although road relay F may be operated cam contacts C8 in the sister controller will not be closed or vice versa and consequently relay G is not operated.

When the solenoid S operates it serves to shunt condensers QA and QB to restore them in readiness for the next timing interval and at springs S3, in conjunction with circuits either thru armatures b2 or b3 it is effective to ensure that without any further operation of the associated road detectors right of way will be returned to the phase from which it has been forcibly removed. In this connection it will be seen from the circuit that if right of way is forcibly removed from phase A relay Fis operated rather than relay E upon termination of the vehicle interval on phase A by operation of maximum relay B, in

which case circuit to energize relay F at the conclusion of this period is completed from minus over cam contact C1, armature b2, relay F to positive. This ensures that in the case of substantially continuous main road traiiic right of way can only be removed from the A phase for very short intervals since it is immediately returned after the expiration of the reduced maximum period. This precaution keeps the main road traffic moving and prevents congestion which would result if it were allowed to tail back across the intersection for a long period. larly, when right of way is forcibly removed from phase B, relay D is energized when the vehicle interval on phase B is terminated by operation of relay B, the circuit extending from minus over cam contact CIS, armature b3, relay D to positive.

The resistances YJ and YK connected in circuit with the road relays D, E and F are de-polarizing resistances which assist in the release of these relays at the correct period. It may happen that the armatures of these relays remain held after the circuit of the coil is opened owing to residual magnetism retained in the core by the presence of a hard spot in the laminations. If this occurs the armature is then forcibly released by arranging for the coil to be connected to the alternating source of supply through one of the resistances YJ or YK which are of such value as to prevent the operation of the coils in series therewith but nevertheless enable sufficient current to flow to bring about the neutralization of the residual magnetism during the appropriate half cycle.

The armatures d3, et and f3 of the road relays D, E1 and F when operated serve to include additional resistance in the amber timing circuit so that when right of way is being forcibly removed an additional amber period is given to facilitate clearing the crossing. If however, this automatic extension feature is not required it may be cut out of service either partially or fully by the operation of one or both of the manual switches AEA or AEB.

The arterial switches RTA and RTB when operated ensure that right of way shall return to the associated phase even in the absence of traffic thereon. Their effect as will be seen from the drawing is to simulate the operation of the detectors at a time when the phase in question is not receiving right of way though they do not produce any extension effect when the phase already has right of way.

The term lane" as used herein designates one or more paths for trafiic movement which may be signalized or accorded right of way as a unit, and is intended to embrace broadly a street, or road or any other form of approach for tramo at an intersection or crossing of lanes as well as a traflic path generally.

Thus the several objects as specifically brought out above, and others, are achieved. It is to be understood that various modifications in the structural details or arrangements of the parts, or changes in the design herein exemplified may be made without departing from the spirit of the invention as defined by the claims.

Having described our invention what we claim as new and desire to secure by Letters Patent of the United States is:

1. In a traffic signal control system for two intersections of cross lanes with a common main traflic lane, a right of way controller at the iirst intersection for according right of way alternate- 1y to the main lane and to the cross lane, a vehicle actuated type of right of way controller at the second intersection and a vehicle actuatable device therefor in the main lane arranged for actuation by vehicles app-roaching said second intersection from said rst intersection, said controller having a normal timing period for the cross lane right of way, and means in the controller at the second intersection operable only when said first controller is according riglit of way to the main lane and said second controller is according right of way to said cross lane for replacing said normal timing period in the sec ond controller with a shorter-than-normal period upon actuation of said vehicle actuatable device in the main lane.

2. In a trafiic signal control system for a plurality of intersections of cross traffic lanes with a common main lane, vehicle actuatable devices in the main and cross lanes at each inter-section, a right of way controller at each intersection for according right of way to the cross lane upon actuation of a vehicle actuatable device in the cross lane for periods of time varying between a minimum and maximum normally in accordance with further actuations of said device and to the main lane upon actuation of a vehicle actuatable device in the main lane, and means in one of the controllers functioning when active only when said controller is according right of way to the cross lane to reduce below normal the maximum timing period in the said controller upon actuation of the main lane actuatable device, and means forming a part of the controller at an adjacent intersection andoperable when said latter controller is according right of way to the main lane to make said rst means active.

3. In a trafiic control system for two intersections of cross lanes with a common main lane including right of way controllers individual to each intersection for according right of way alterna ely to the main and cross lane, a traffic actuatable device in the main lane at one ntersection, means forming a part of the controller at said one intersection to provide a maximum right or" way period for the cross lane at said intersection, and control means when operable functioning in response to actuation of the said traffic actuatable device during said cross lane right of way period to reduce said maximum period, and means forming a part of the right of way controller at the other intersection and operable only when said controller is according right of way to the main lane to make Said coritrol means operable.

Ll. In a tramo signal control system for two intersections of cross lanes with a common main lane including trafc actuated devices in the main and cross lanes at each intersection, right of way controllers individual to each intersection for according right of way alternately to the main lane and cross lane between minimum and maximum periods in accordance with traiic operation of said traffic actuated devices in the cross lanes, and means forming a part of the right of way controller at said first intersection operable upon said controller according right of way to the main lane to prepare a control circuit to said second intersection right of way controller for reducing the maximum period on the cross lane at said second intersection, and further means operable responsive to actuation of a main lane trac actuated device at the second inter- 75 section during the cross lane right of way period at said second intersection to complete the said control circuit.

5. A traiic signal control system for two intersections of cross lanes with a common main lane including in combination a right of way controller at the first intersection and a similar right of way controller at the second intersection each such controller adapted to accord right of way alternately to the main and cross lanes at its intersection, vehicle actuatable devices in the main and cross lanes at said second intersection and associated with the controller thercat` said latter controller upon actuation of its associated vehicle actuatable device in the cross lane according right of way to the cross lane for a period variable between a minimum and a maximum in accordance with actuations of such latter device, and means in the controller at the second intersection operating only when said controller at the first intersection is according right of way to the main lane and said controller at the second intersection is concurrently according right of way to the cross lane for reducing the cross lane maximum period upon actuation of the vehicle actuatable device in the main lane at said second intersection by a vehicle approaching from said rst intersection.

6. In a traino signal control system for two intersections of cross traffic lanes with a common main lane, the combination of traffic actuatable devices in the main and cross lanes at each intersection, a right of way controller at each intersection operable in response to actuation of said devices to accord right of way to the main lane and cross lanes alternately between normal minimum and maximum periods in accordance with actuation of said devices, means associated with the controller at one intersection and operable in response to actuation oi' the traific actuatable device in the main lane at Said one intersection to shorten to less than normal the maximum right of way period in the cross lane at said one intersection, and means associated with said controllers for causing said last named means to be so operable only while right of way is being accorded to the cross lane at said one intersection and right of way is being concurrently accorded to the main lane at the other intersection.

7. In a traffic signal control system for two intersections of cross trailic lanes with a common main lane, the combination of traflc actuatable devices in the main and cross lanes at each intersection, a right of way controller at each intersection operable in response to actuation of said devices to accord right of way to the main lane and cross lanes alternately between normal minimum and maximum periods in accordance with actuations of said devices, means when operable functioning in response to actuation of the traffic actuatable device in the main lane at one intersection to shorten to less than normal the maximum right of way period in the cross lane at said one intersection, and means at the other intersection functioning when right of way is accorded to the main lane at the latter intersection to make said last named means so operable.

8. In a traffic control system for two intersections of cross lanes with a common main lane including in combination right of way control- 1ers individual to each intersection for according right of way alternately to the main and cross lanes, timing means for governing the time periods of such according of right of Way, said timing means including a condenser, a resistance, means for charging said condenser at a time rate determined by said resistance when right of Way is accorded to said cross lane, and means operable upon said condenser receiving a predetermined charge to terminate right of way in said cross lane and thus provide a maxi mum right of way period for the cross lane, said combination also including a traic actuatable device in the main lane at one of said intersections, and control means when operable fnnctioning in lresponse to actuation of said device during said cross lane right of way period at said one intersection tofreduce said maximum f`l period by varying* said resistance, and means 9. In a trahie control system for two intersections' of cross lanes with a common main lane including in combination traiiic actuated devices in the main and cross lanes at each intersection, ight'of way cont-rollers individual to each intersection for according right of way alternately to the main land cross lanes between minimum and maximum periods in accordance with traffic operation of said traic actuated devices in the respective main and cross lanes, timing means for providing the said maximum period on the cross lane and comprising a condenser, charging means for said condenser including a resistance for controlling the time rate of charge, and means operable upon said condenser receiving a predetermined charge to terminate the said maximum period of right of way in said cross lane, the combination also including control means associated with the controller at said one intersection and functioning when operable in response to operation of a main lane traiiic actuated device at said one intersection to shorten the cross lane maximum period by altering the resistance in said timing means thereat, and means forming a part of the controller at the other intersection and operable when said latter controller is according right of way to the main lane to make said control means operable.

10. In a traic control system for two intersections of cross lanes with a common main lane including in combination traffic actuated devices in the main and cross lanes at each intersection, right of way controllers individual to each intersection for according right of way alternately to the main lane and cross lanes between minimum and maximum periods in accordance with traflic operation of said traic actuated devices in the respective main and cross lanes, a control circuit capable of being prepared for completion and then completed to the controller at the second intersection, means forming a part of the controller at the first of said intersections and operating responsive to actuation of a main lane traflic actuated device at said rst intersection occurring during the cross lane right of way period at said first intersection to prepare said control circuit to said second intersection right of way controller withn in a time period from such actuation substantially corresponding with such maximum, means associated with said second controller and operated by completion of said control circuit for reducing the maximum period on the cross lane at said second intersection, and further means operable responsive to actuation of a main lane traiiic actuated device at the second intersection during the cross lane right of Way period at said second intersection to complete the said control circuit.

11. A traffic control system for two spaced int :sectionsof cross lanes with a common main lane including in combination a right of way controller' for each intersection adapted to accord right of way alternately to the main and cross lanes at its intersection, each of said controllers including switching mechanism having a plurality` of positions through which it is adapted to be operated step by step for so according right of way alternately to the lanes and timing means operated by said mechanism in each step to shift said mechanism to the next step after a time interval and thus to time such a"- cord oi.' right of way, said timing means comprising a condenser, an electronic tube having a threshold voltage below which it is non-com ducting and above which it is conducting to pass current, means including a relay operable for so shifting said mechanism from one step to another, means including a resistance for charging said condenser to the threshold voltage of said tube at a time rate determined by said resistance whereupon said tube passes current to operate said relay, said combination also including traffic actuatable devices in the lanes and connected to the respective controllers at the respective intersections, means forming a part of said controllers for varying such accord of right of way between minimum and maximum periods determined by said timing means in accordance with actuations of said devices, a control circuit capable of being prepared for completion and then completed to the controller at the second intersection, means operable upon accord of right of way to the cross lane by the controller at the rst intersection to prepare said control circuit to the controller of said second intersection, means forming a part of the controller at the second intersection and operable upon actuation of the traic actuatable device in the main lane at said second intersection to complete said control circuit, and means in the second controller operable when said circuit is completed during the cross lane right of way period at said second intersection to reduce the maximum cross lane right of Way period at the said second intersection by altering the charging resistance in said second controller.

12. In a traffic signal control system forv two intersections of cross trai'c lanes with a com.- mon main lane, the combination of right of. Way controllers at the respective intersections adapted to accord right of Way alternately to the main and cross lanes at the respective intersections, a traffic actuatable device in the main lane at one intersection arranged for actuation by traiic approaching said one intersection from the other intersection, means forming a part of the controller at said one intersection and including a timing element initiated by actuation of the said device when the said controller at said one intersection is according right of Way to the cross lane thereat to provide a normal max imum time limit to such accord of right of way to the cross lane, and means connected with said timing element and with said controller at the other intersection and operable only when said latter controller is according right of way to the main lane to reduce the said cross lane time limit caused by such actuation to less than normal.

13. In a traiiic signal control system for two intersections of cross traffic lanes with a common main lane, the combination of right of way controllers at the respective intersections adapted to accord right of way alternately to the main and cross lanes at the respective intersections, a traic actuatable device in the main lane at one intersection arranged for actuation by traic approaching said one intersection from the other intersection, means forming a part of the controller at said one intersection and including a timing element operated by actuation of said device when the said controller at said one intersection is according right of way to the cross lane thereat to provide a normal maximum time limit to such accord of right of way to the cross lane, and control means connected with said timing element for reducing said maximum time limit when said control means is operable, and a circuit connected to said control means and including means in the controller at the other intersection operating only when said controller at said other intersection is according right of way to the main lane for making said control means operable.

14. In a trahie control system for two intersections of cross trafic lanes with a common main lane including in combination traffic actuated devices in the main and cross lanes at each intersection, right of way controllers individual to each intersection for according right of Way alternately to the main and cross lanes between minimum and maximum periods in accordance with traic operation of said traffic actuated devices in the respective main and cross lanes, timing means forming a part of the controller at one intersection for providing such maximum period on the cross lane at said intersection, said timing means having an operating circuit and a resistance therein and adapted to have its time period varied by variation of said resistance, control means associated with said controller at said one intersection for varying when operable said resistance to shorten the cross lane maximum period in response to operation of one of said devices on the main lane at said one intersection by traic approaching from the other intersection, and means forming a part of the controller at the other intersection and connected to said control means and operable only when said latter controller is according right of Way to the main lane to make said control means so operable.

THOMAS PHILIP PREIST. ALFRED PERCY BAILEY REN SHAW. 

